Thermodynamic Limit of Exciton Fission Solar Cell Efficiency

A detailed balance chemical kinetic model is applied to exciton fission in photovoltaic devices. Energy conversion efficiency limits are found to be significantly higher than previously calculated. We lift unnecessary restrictions on the relative energies of the electronic states involved and show that the entropically favorable nature of the exciton fission process can be harnessed to bring about higher energy conversion efficiencies. By accounting for endothermic fission, the calculated limiting efficiency of a device is increased from 41.9 to 45.9% under standard conditions. By considering the exciton binding energy in organic cells efficiency limits of around 40% are calculated.